Inverter for running fridge while traveling

[dronning]

Thinking of adding a 12v to 120v inverter to run the fridge (Gas/AC) on long trips. Is this a waste of time?

I can't find the watts or amps for the fridge but I remember reading somewhere the heating element used less than 400W. I have both a 500W & 2000W inverter from previous projects. If the demand/draw is 600W is there any up or downside from running the 2000W inverter?

- Dave

[SeaDog]

Most two way units cool super on propane and use very little propane in the process. If on a long trip you run the risk of depleting your battery unless you have a charging source. Myself I don't see gain in doing the inverter thing on a two way frig.

[timfromma]

Run it on propane, that's what it's designed for. You will deplete your batteries rather quickly and your TV will not supply enough power to keep them charged.

[Thurman]

Before packing for a trip I always start up the fridge on 120vAC at least two days in advance. Fortunately I have a fridge in my shop where we put anything that is going into the camper fridge to cool it down before placing in the camper fridge. Everything goes in the camper fridge the day before we leave while the fridge is on shore power, so everything should be cooled. I have traveled up to three (3) hours without using the LP on the fridge and had no problems. I have also traveled with the fridge on LP up to three (3) hours with no problem.

[rockfordroo]

I agree with running on propane.

But if you're committed to this, the Dometic 2652 uses 325 watts. See page 2 of attached. Most other models, unless it's a 4 door, should be in the same ballpark.

[wcrafter]

Use the propane side it will cool great....

[bikendan]

Waste of time installing an inverter, when you can simply run it on propane while traveling.
The VAST majority of RVers do this with confidence.

[JLeising]

I haven't done this mod, but have thought about it and have done a little experimenting.
First - as to need - We did an Alaska trip in 2013 where we went part way by ferry. The ferry required propane off. We had the fridge off for probably 10+ hours in the hold of the ferry - everything stayed frozen in the freezer and plenty cold in the fridge. True, this was a benign temp environment in the hold and the fridge door was never opened, but both the fridge and freezer temps were well maintained - this experience made doing this mod less attractive to me.

I have a 400 watt pure sine wave inverter installed for other reasons. I tried plugging the fridge into it as an experiment. The fridge worked, but the inverter low voltage alarm "blipped" on and off. Suspect I would need larger inverter-to-battery wires to support the load of the fridge.

Also thought about how to wire it should I decide to add the inverter power option to the fridge. Ideally, the fridge would run on AC power when shore or generator power is available; propane when no shore/generator AC; and inverter AC when no shore power, generator power or propane available. Complicated. I would probably choose to manually switch the plug over to the inverter output on the rare occasion I wanted to run the fridge off the inverter.

Pulling 300+ watts from the inverter probably pulls ~35 amps from the batteries. Although a pre-cooled fridge would only run 25% to 50% of the time, still quite a battery drain if more than a couple of hours (4 hours at 50% duty cycle and 35 amps draw would deplete 70 amp-hours of battery capacity). Would only want to run for short periods without a source of battery charge - and, based on my Alaska ferry experience, the fridge can maintain temp for short periods without running ...

Driving the motorhome (with the vehicle alternator to maintain the house batteries) for, say, 10 hour days in the desert (high ambient temp) - if unwilling to drive with the propane on for safety reasons - might rationalize the mod.

FYI, Jim

[br23mat8]

Doesn't the propane refrig. have to have a little juice to power the igniter for the propane to lite??

[ependydad]

Originally Posted by br23mat8

Doesn't the propane refrig. have to have a little juice to power the igniter for the propane to lite??

Yes, but that’s 12v power and comes directly from the battery. No inverter needed if running on propane.

[jimmoore13]

Here's how you know the AC demands of your fridge through a 12 volt to 120 volt inverter: https://www.rapidtables.com/calc/ele...alculator.html

Using someone's estimate (above) of 325 watts to run the fridge, and remembering that all calculations in the equation are based on 12 Volts...not 120 Volts...your fridge will draw 27 amps when running. For argument's sake, assume a 50% duty cycle....it's running half the time. So that's 27 amp hours over the course of 2 hours on the road. Time is the enemy here, so if you're on the road 8 hours, that's over 100 amp hours to run the fridge.

Let's not forget that an inverter is not 100% efficient. For back of the envelope calculations assume 10% waste, so the fridge and inverter together will consume 30 amps when running the fridge and about 2.5 amps (+/-) when the inverter is idling. (Again, ESTIMATES.)

Now let's assume you have a somewhat common battery configuration: a 12-volt group 24 or group 27. The group 24 has a MAX capacity of about 80 amp hours. The Group 27 might go 100. But to keep from ruining the battery, you should only consume about half of that...40 (or 50) amp hours. See where this is going?

So, a bit more that 2 hours from home, your battery is effectively dead. Your rig needs to be connected to shore power or a generator to revive the battery...and that's just 2 1/2 hours down the road. Your 8 hour trip will probably destroy the battery by over-discharging it.

But what about the charge from the tow vehicle? Estimates vary on how much charging power can be delivered through your 7 pin connector to the trailer battery. For argument's sake, let's assume 5 amps...could be up to about 7. There are many variables affecting this, but that 7 pin connector is not wired with #8 or #10 wire directly from the battery to the connector, and it's probably fused at 10 amps at most. There's no magic way to make the TV deliver 30 amps of charging power at 12 volts.
If you're pulling 30 amps out of the battery to run your fridge and replacing it with 5 amps, you buy some time, but not much.

As virtually everyone else has said, go with the propane. If you want an inverter for other purposes, the info above will help you know how to manage your expectations. I have solar with the capacity to fully charge my battery by midday, so I go to bed with a full charge. I have a 400 watt inverter that I use to run my 360 watt electric blanket for 1/2 hour to take the chill off the bed. That eats about 15 amps (30 amp load for 1/2 hour = 15 amp hours). The remaining 40 amps in my group 24 battery go to the furnace, water heater ignition, and water pump. The battery stays healthy, and then the sun comes up.

P.S. I had a 3-way tiny fridge in my first PUP. I'd try to run the fridge on 12 volt power going down the road, and over the course of a 2 hour trip, even with the trickle charge from the TV, my battery would be seriously depleted when I got to the campsite. Flooded batteries are very poor (low density) energy storage devices. Propane, on the other hand, stores a HUGE amount of BTUs in a tiny quantity of LP. (Gasoline is even more energy dense, which accounts for why dual-fuel generators deliver LOTS more power on gasoline than propane.)

My fridge routine is to start the fridge on shore power the night before departure. This cools the fridge cabinet. I stock the fridge exclusively with cold items...no warm beer...a couple hours before departure, and let shore power stabilize the fridge temp. About an hour before departure, I manually switch the fridge to propane to ensure it's working correctly. I disconnect shore power at the last minute. This leaves my battery topped off and the fridge cold.

Finally, if you're concerned about running propane going down the road, a cold fridge full of cold food/drinks will maintain temp for several hours with no power. They're pretty good ice-boxes. If you stop along the way, fire up the fridge on propane to cool it, then shut down when you continue on your way.

[RECONUSMC]

This 3500 unit from Harbor Freight is same model Northern Tools sells. This along with installing the EASY START on your AC will run everything. Instead of the AC starting at 45Amps it gradually comes up from 5 Amps to running and the 3500 does it well. https://www.microair.net/collections...-soft-starters How to Video:

https://www.youtube.com/watch?v=soP0uZFd0nQ

Generator https://www.harborfreight.com/3500-w...tor-63584.html on sale sometimes for about $649.00

Hope this helps

[Larry-NC]

Originally Posted by timfromma

Run it on propane, that's what it's designed for. You will deplete your batteries rather quickly and your TV will not supply enough power to keep them charged.

Be sure you don't park on a hill for an extended time when running on propane. These refrigerators are designed to be operated in a generally level condition. Going up/down steep hills won't cause difficulties but parking overnight on a hill could ruin the refrigerator.

Larry

[timfromma]

Originally Posted by Larry-NC

Be sure you don't park on a hill for an extended time when running on propane. These refrigerators are designed to be operated in a generally level condition. Going up/down steep hills won't cause difficulties but parking overnight on a hill could ruin the refrigerator.



Larry

Any hill steep enough to harm the fridge will be make for very uncomfortable sleeping. If the camper is level enough for you to be comfortable, it's level enough for the fridge.

[Canadiancrew]

I don't understand the issue. Just run the propane. Have done so for 30 years and many tens of thousands of miles. No worries about running batteries down while parked for lunches or whatever. You won't have enough battery for an inverter.

[garbonz]

Originally Posted by timfromma

Any hill steep enough to harm the fridge will be make for very uncomfortable sleeping. If the camper is level enough for you to be comfortable, it's level enough for the fridge.

3 degrees side to side (fridge directions not RV) is the biggest problem and if your frig is oriented front to back that ain't very much. The deterioration of the refrigerant takes place over many cycles and may not manifest itself for a couple years, but it will eventually. Not hard to use a level and 3 deg is about half a bubble typically.

[bikendan]

Originally Posted by RECONUSMC

This 3500 unit from Harbor Freight is same model Northern Tools sells. This along with installing the EASY START on your AC will run everything. Instead of the AC starting at 45Amps it gradually comes up from 5 Amps to running and the 3500 does it well. https://www.microair.net/collections...-soft-starters How to Video:

Generator https://www.harborfreight.com/3500-w...tor-63584.html on sale sometimes for about $649.00

Hope this helps

What's this have to do with running a fridge on the road?🤔

[Larry-NC]

Originally Posted by timfromma

Any hill steep enough to harm the fridge will be make for very uncomfortable sleeping. If the camper is level enough for you to be comfortable, it's level enough for the fridge.

The reference for my post above was an article in another forum some months ago. The travellers had parked on a steep hill and gone inside to spend the night with friends. The refrigerator was destroyed. They wrote that an installed replacement cost them $1000.

[JLeising]

With regard to refrigerator damage from running out-of-level, don't think it matters if the fridge is run on propane or on electric...

[GmanHawaii]

Originally Posted by timfromma

Run it on propane, that's what it's designed for. You will deplete your batteries rather quickly and your TV will not supply enough power to keep them charged.

I have two batteries and a whirlpool side by side, drove 10+ hours from Oklahoma to Albuquerque and didn't drain my batteries.